To cut relatively large diameter holes in a work piece, made of wood, metal or other material, a hole saw is often used. A hole saw is a cylindrical saw having teeth along its lower circular cutting edge and a top. The hole saw is mounted to a coaxially positioned pilot drill by a mandrel fastened within a hole formed in the top of the hole saw. The hole saw, mandrel and pilot drill are, in this application, collectively termed a hole saw assembly. Several different sizes of hole saws can be used with a single pilot drill and mandrel.
The pilot drill extends past the cutting edge of the hole saw so that a pilot hole is drilled into the material first before the hole saw begins to remove a circular plug of material from the work piece. The pilot drill thus keeps the hole saw properly positioned while the hole saw starts its cut. This need for positioning by the pilot drill is necessary when the hole saw is used with hand-held drills. Otherwise, especially when cutting a hard material such as metal, the hole saw would have a tendency to walk around the work piece when starting to cut the hole.
Once a hole is already cut into the work piece, if the hole is improperly positioned or is too small, or both, difficulties arise. That is, if a new hole is to be cut in the work piece, there is no longer any material for the pilot drill to cut into to guide the hole saw. In these situations it has generally not been possible to use a hand-held drill mounted hole saw to create the additional hole.